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Resident Nutcase
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Discussion Starter · #1 ·
I started out over ten or twelve years ago with an old Trumark wrist rocket someone gave me. While layed off for the winter I decided to get some new bands and shoot it in the apartment I lived in. Small, compact, and pretty quick, I found out when shooting cardboard box targets I got bored with it pretty quick. After a while it didnt seem much fun even after I got fairly good with it. Just no WOW!!! factor I guess. I couldnt even tell where I had hit half the time. So like everyone else I started experimenting, wanting something more "powerful" - more punch I guess.

One night after watching the news about the ROM collection of crossbows, the curator explained about the effeciencies of the crossbow, and I got to wondering about what she meant about being effecient, and wondered if I could apply those same principals to the slingshot. So I started playing around with the idea, comparing it to my archery experiences. I was only moderately accurate, hated the huge upfront expense, and the fact if you bent, damaged, or lost your arrows you had to buy some more $$$$$$. Worst of all all you could go is target shoot or hunt - no off-hand plinking. It was too much like golf. Aim shoot and go fetch. The bow soon got put in the closet. I also thought it was kinda slow and the range kinda sucked.

So, I decided to see if I could blend the best features what I liked about the bow, and the best features I liked about the slingshot. I've been building them ever since. In evaluating the slingshots use of applied force, it didnt take a rocket scientist to figure out it was transferred to the wrist and thus wasted. So the best way to increase effeciency, was to replace the Y shaped yoke with something that was able to take that wasted energy and transfer it into motion. Namely increasing the amount of applied force or power to the projectile.

So thats how I got started, and it appears I was not alone in my quest,because a fella in the states by the name of Stan Wing was working along the same line of thinking as me. I dont think its any accident that both our designs are inswingers.

Anyhow, STan love of working with rubber or latex resulted in him developing patenting and marketing the Slingshot Rifle. I went another route in my work, going with steel springs. I wanted something I could use in the dead of winter to go hunt rabbits and such, and later on enlarged the idea to something suitable for big game.
So the Springslinger was the beastie I invented , very similar to a the compound design on the new Compounding slingshots thread.

But guess what? Slingshotter's dont like compounds. I joined Mels group many years ago and found that out very quickly. Still, I kept using mine in the basement over the past 10 years since I bought my house. I've put many a hole in the cement walls from bad shots, love to blow up stuff with it in the basement, and once cut an old broken washing machine clean in half with it. Took about a thousand shots LOL.

Now I concentrate on building ballista's. Torsion powered machines of all types, but am concentrating on whats called a manuballista, or hand held ballista. Not many people are even aware of their existance, never mind the in-swinging model. Im developing a bolt on kit for crossbows, and am almost there. I've had a few nibbles from crossbow manufacturers, so hopefully if everything goes right, you can buy one in a year or two, maybe sooner.

And all of this from what started as a design exercise for my slingshot. Anyway, thought I'd share the history behind my work and blog before you visit. I hope you enjoy my blog and theres lots of science goodies for you there too!

http://warhammer1.wordpress.com/2009/08/21/hello-world/?preview=true&preview_id=1&preview_nonce=5089f90167
 

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Resident Nutcase
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Discussion Starter · #2 ·
Hey folks.

Just a few lines to update on my ballista - ing. Since time, health, and finances are against me for a while,I have been been trying to get a fellow torsion ballista freak to try some of my ballista innovations and innovative designs. The only real difference here is that he uses rope bundle tech. while I think modern spring steel (and compounding or cammed ballista's) would be much better(faster). For now he wont budge on the rope bundle thing as he is into experimental archeology regarding ballista's.

My overall goal is to get him to use heavier projectiles (10,000 grains and up)as his machine will handle 5000lbs pull with ease,
and without the use of pulleys, cams, (or compounding) meet or exceed that of the new Scorpyd RDT 165 capable of 465 fps with a 350 grain arrow or 425 fps with a regular 400 grain plus arrow. (Its a speed thing and an engineering challenge) LOL.

anyhow, its as much a challenge to get him to try my designs as it is in re-engineering 2000 year old technology and materials to exceed modern day crossbow performance.

So far I have got him to using 7000 - 8000 grain bolts(he used to use 2855 grain bolts), and into using less than 90 degrees of limb rotation (110-115 degrees is normal for an inswinger). while not confirmed by a duplication in performance, the best speed so far is 402 fps using a 7500 grain bolt, approximately 75 degrees rotation, and approx. 4700lbs pull weight. Draw length was just under 50 inches if I remember correctly. Energy was just over 2700 foot pounds which is a whole lot of Joules.

Here's a link to our little "experiments" as I slowly get him up to speed on innovative approaches to velocity and unreal KE. Utilizing some of my design changes, we should see a whole new level of performance in another month or so after he completes the new parts and changes in design - very minor really.

I consider myself fortunate in that he is actually open minded enuff to consider my outlandish claims and design features. His work is important as it will either confirm or invalidate my design changes as having superior performance over the best the old world machinery. Most scholars that I have shared my ideas with consider them rubbish. There are a few here who would agree I tend to rub folks the wrong way anyhow...Aim high and shoot straight.

Anyhow, heres the link: http://wattsunique.com/blog/?p=3501#comments My nickname on his blog is CApt Harpoon from my propensity for large, long, and heavy projectiles.

BTW - some nice vids there shooting egg sized lead projectiles of 6000 grains, making it kinda the granddaddy bad ass slingshot (before rubber or latex invented LOL).

W.
 

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WH , thank you bringing this back up top. While I am not an enthusiast in the sense that I have siege machines in my basement- I do love to read about the mechanical and technological aspects of them and always have.
Who knows where that may lead me
 

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Thanks for the encouragement and comments, I dont seem to have made many friends here LOL. Seems a few here a finally getting around to exploring the inswinging designs I tried to interest folks in. Stop by and visit my blog from time to time. I used to be interested in finding a manufacturer for my crazy designs, with the torsion slingshot my very favorite for fun, shock, and awe. The feedback here indicates perhaps that would be a waste of time, something I am running out of.

The slingshot design is also great for those with physical handicaps. Normally when you pull back on powerband, energy is transferred to hand wrist fingers etc. Offsetting the handle and forks allows the handle to act as a pivot point, transferring the main force away from the hand and wrist, turning the linior force or pull into a horizontal movement at the end of the armvbrace, so much of the force is used to hold the weapon in place snug against the arm.

It is held loosely in the hand like a bow to avoid torquing. Even if a fellow had no fingers/hand at all, he could still shoot my springslinger. Like a bow it shoots hole in hole, and is able to utilize sighting devices if wished. I like bows, but you cannot go "plinking" with five dollar arrows. So this is my alternative (torsion slingshot)to a regular archery bow. Its hard to run out of ammo with this one, but targets and backstops are another thing as they are literally shredded.

http://warhammer1.wordpress.com/

WH , thank you bringing this back up top. While I am not an enthusiast in the sense that I have siege machines in my basement- I do love to read about the mechanical and technological aspects of them and always have.
Who knows where that may lead me
 

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What is the purpose of combining let-off with a release mechanism?
 

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Discussion Starter · #6 ·
Without the let off, it would load past the draw loc's manufacturers recommended pull capacity. Without the draw loc or any trigger release the string angle is too acute to finger shoot past 20lbs pull.

The machines in the pics are about 12 years old. The dual pulley one is actually a work platform that allows many uses and string configurations. One would be exactly like the Gearhead bow and crossbow lever pulley arrangement, and another would be a new proposed crossbow coming to the market soon. The Ghetrax by Tecnarm.

I chose to go with the design that had the highest performance and was the most FUN to shoot. Nice you noticed the built in let-off.

By simply removing the pulleys and changing the string, the little bow would have 120lbs pull(non-compounding), but only a 14 inch draw. 65lbs pull is about as high as I want to go in a bow mode, so the let-off lets me continue to load potential energy into the machine well past 90 degrees of rotation. More rotation, more energy to pump into the projectile.

The thing about an inswinging design is that about 50% of total draw length is accomplished within the first 35-40 degrees depending on axle to axle spacing and arm length. Simply put, the string and mass must double its speed during the last 35 degrees. Therefore, the faster (more rotation) I apply, the more potential I load into it.

The little slingshot with pulleys will actually load past 180 degrees (bad - ouch!). Later I engineered in a rock solid back wall to prevent this. I never have to worry about the bands snapping back in my face. Should damage occur that I dont notice and it snaps, its always at the end of the stroke. Often I wont know it has snapped until I try to load it again.

I figure with replacing the lower levers with a simple pulley, I could squeeze an estimated 190-195 degrees. But why bother? its fast enough for me, and provides the all important fun factor shredding any kind of target.

I like the fletchette idea, and my slingshot is perfect as powerbands are not even necessary. Two pieces of string/cord will do, and should still be able to ventilate most anything you hit. Thank you for showing interest.

What is the purpose of combining let-off with a release mechanism?
 
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